Extra Kollsman Altimeter Poimters

[[email protected]]

I have an old Square D Kollsman 3 pointer altimeter that I think it's
about 50 or more years old and seems to be in working condition. The
body is about 2 13/16 diameter. The label on the back says part no.
371K-05

The three altitude pointers give the usual altitude readout. The little
Kollsman barometer window works and I know how to synchronize a known
altitude with the known barometer pressure by removing the little screw
and pulling the Kollsman knob out for the 'calibration'.

Now here's my question. There are two extra little visible pointers on
this altimeter that both rotate around concentric circles centered on
the instrument face. What are these pointers for. One is on the outer
circumference of the dial and the other one is on a smaller inner
circle with a radius of about 1 inch. Both pointers rotate when the
Kollsman knob is turned. They do NOT respond to air pressure changes.
The outer one moves at the same rate as the hundreds altimeter pointer
when the knob is turned. The inner pointer increments 100 feet when the
outer pointer makes one complete revolution around the face.

What are these "extra" pointers for???? They seem to serve no other
purpose than measuring the rotation of the Kollsman knob.

Dennis

[Icebound]

> wrote in message
oups.com...
>I have an old Square D Kollsman 3 pointer altimeter that I think it's
> about 50 or more years old and seems to be in working condition. The
> body is about 2 13/16 diameter. The label on the back says part no.
> 371K-05
>
> The three altitude pointers give the usual altitude readout. The little
> Kollsman barometer window works and I know how to synchronize a known
> altitude with the known barometer pressure by removing the little screw
> and pulling the Kollsman knob out for the 'calibration'.
>
> Now here's my question. There are two extra little visible pointers on
> this altimeter that both rotate around concentric circles centered on
> the instrument face. What are these pointers for. One is on the outer
> circumference of the dial and the other one is on a smaller inner
> circle with a radius of about 1 inch. Both pointers rotate when the
> Kollsman knob is turned. They do NOT respond to air pressure changes.
> The outer one moves at the same rate as the hundreds altimeter pointer
> when the knob is turned. The inner pointer increments 100 feet when the
> outer pointer makes one complete revolution around the face.
>
> What are these "extra" pointers for???? They seem to serve no other
> purpose than measuring the rotation of the Kollsman knob.
>
> Dennis
>

Is it possible that they correspond to hundreds and thousands of feet of
*pressure*-altitude? Do they both go to zero and zero, when you set the
Kollsman to 29.92???

[[email protected]]

Is it possible that they correspond to hundreds and thousands of feet
of
*pressure*-altitude? Do they both go to zero and zero, when you set
the
Kollsman to 29.92???

No. When the Kollsman is set to 29.92, the little pointers indicate
1,740 feet. I almost think they may be for some sort of maintenance
purpose.

[RST Engineering]

Then somebody got the little setscrew loose from the bottom of the Kollsman
knob and dicked the hands to read 1740. Or YOU are at 1740 density
altitude, one of the two.

When the Kollsman is set to 29.92 the hands should read your MSL altitude
corrected for nonstandard temperature and nonstandard pressure, or density
altitude (which is the same thing). You can readjust the altimeter by
calculating the density altitude at the altimeter's location, removing the
setscrew from the bottom of the Kollsman knob, pulling the knob out, and
making the altimeter read the density altitude with the window remaining at
29.92.

If you don't want to go through the hassle of doing all the calculations,
go into the FBO to the calibrated altimeter they use to give the altimeter
setting, set it to 29.92, put your altimeter on the same bench or table, and
adjust your altimeter to read exactly what the FBO's altimeter reads.

In either case, don't forget to replace the setscrew.

Don't ever make the mistake of telling somebody you reCALIBRATED your
altimeter because calibration requires an instrument shop to do the
calibration. You ADJUSTED it, which is quite legal to do.

Jim



> wrote in message
oups.com...
> Is it possible that they correspond to hundreds and thousands of feet
> of
> *pressure*-altitude? Do they both go to zero and zero, when you set
> the
> Kollsman to 29.92???
>
> No. When the Kollsman is set to 29.92, the little pointers indicate
> 1,740 feet. I almost think they may be for some sort of maintenance
> purpose.
>

[Icebound]

"RST Engineering" > wrote in message
...
> Then somebody got the little setscrew loose from the bottom of the
> Kollsman knob and dicked the hands to read 1740. Or YOU are at 1740
> density altitude, one of the two.
>
> When the Kollsman is set to 29.92 the hands should read your MSL altitude
> corrected for nonstandard temperature and nonstandard pressure, or density
> altitude (which is the same thing). You can readjust the altimeter by
> calculating the density altitude at the altimeter's location, removing the
> setscrew from the bottom of the Kollsman knob, pulling the knob out, and
> making the altimeter read the density altitude with the window remaining
> at 29.92.


Uh... excuse me?

Are you saying that the main "altitude" pointer that we all know and love is
what is indicating a *density* altitude?

Or are you saying that the *second* (unknown) set of pointers referenced by
the OP should be indicating a density altitude?

Either, if true, implies that this instrument has outdoor temperature
sensing???

[Icebound]

> wrote in message
oups.com...
>I have an old Square D Kollsman 3 pointer altimeter that I think it's
> about 50 or more years old and seems to be in working condition. The
> body is about 2 13/16 diameter. The label on the back says part no.
> 371K-05
>
> The three altitude pointers give the usual altitude readout. The little
> Kollsman barometer window works and I know how to synchronize a known
> altitude with the known barometer pressure by removing the little screw
> and pulling the Kollsman knob out for the 'calibration'.
>
> Now here's my question. There are two extra little visible pointers on
> this altimeter that both rotate around concentric circles centered on
> the instrument face. What are these pointers for. One is on the outer
> circumference of the dial and the other one is on a smaller inner
> circle with a radius of about 1 inch. Both pointers rotate when the
> Kollsman knob is turned. They do NOT respond to air pressure changes.
> The outer one moves at the same rate as the hundreds altimeter pointer
> when the knob is turned. The inner pointer increments 100 feet when the
> outer pointer makes one complete revolution around the face.
>
> What are these "extra" pointers for???? They seem to serve no other
> purpose than measuring the rotation of the Kollsman knob.
>
> Dennis
>

Does this sound right?
http://ww2airfronts.org/Flight%20School/advanced/Navigation/nav_deadreck.html

(then search the page for "reference markers")

Have you tried turning the Kollsman past its high limit (31.00??) or below
its lowest limit???

The implication of the article is that the reference markers are used to set
the altimeter setting when it is out of the range of the Kollsman window.
In other words, if you know your airport is 7,000 feet, and the pressure is
very high, say such that your altimeter setting would be 31.15.

You cannot set 31.15 in the Kollsman, but if you are sitting on the ground
at a known 7,000 feet, you can turn the reference markers to 7,000, and your
altimeter is now set correctly....

As I read the article, anyway....

Presumably, those markers would be a double check of the altimeter's
calibration. If on the ground, setting the markers to the station elevation
should give you the correct elevation of the station on both the read-out
and the reference markers. When in the air and obtaining an Altimeter
setting, setting the value should move the markers to the station's
elevation... a double-check that you did not mis-set a digit.

..... again, that's my understanding of the article....

[[email protected]]

Icebound,

I think you are getting close to the answer and thanks for the link to
a pretty good site. Indeed if I turn the Kollsman setting below 29.70,
a black shutter comes across the little window making any setting lower
than 29.70 impossible. If I turn it above 31.00, the Kollsman dial
markings go blank until they resume again at 28.10. But I'm still
confused.

I am at an actual known altitude of about 20 feet above sea level here
where the altimeter sits on my desk beside me. If I set the Kollsman
window to the current barometer setting, then the hands show nearly 20
feet as expected. The "reference pointers" indicate an altitude that
is dependent on the Kollsman window setting.

For example, today the barometer setting is 30.10, the hands say 20
feet and the reference pointers show about 1,580 feet. Now what
exactly is 1,580 feet telling me?

[Icebound]

> wrote in message
ups.com...
> Icebound,
>
> I think you are getting close to the answer and thanks for the link to
> a pretty good site. Indeed if I turn the Kollsman setting below 29.70,
> a black shutter comes across the little window making any setting lower
> than 29.70 impossible. If I turn it above 31.00, the Kollsman dial
> markings go blank until they resume again at 28.10. But I'm still
> confused.
>
> I am at an actual known altitude of about 20 feet above sea level here
> where the altimeter sits on my desk beside me. If I set the Kollsman
> window to the current barometer setting, then the hands show nearly 20
> feet as expected. The "reference pointers" indicate an altitude that
> is dependent on the Kollsman window setting.
>
> For example, today the barometer setting is 30.10, the hands say 20
> feet and the reference pointers show about 1,580 feet. Now what
> exactly is 1,580 feet telling me?
>

Well, if we *are* correct, it could be something as simple as:

....you would think that the reference-indicators, too, would have some sort
of adjustment screw hidden away somewhere. Perhaps somebody before you
wondered about it and fiddled with them. If you can find it and "correct"
the indicators to 20 feet independently of the Kollsman knob.... that may be
the answer.

[[email protected]]

Well, I removed the innards and (independently) reset the reference
pointers to agree with the altitude hands at the correct Kollsman
setting. (I'm pretty handy at tinkering with delicate instruments.)

But I still don't really know what those little markers are for. If, as
you have suggested, they are used to set the altimeter to the correct
barometric pressure when the Kollsman window is blanked out, how does
one know where to set the markers? Let's say one is in an area where
the altitude-barometer combination there renders the Kollsman window
useless. If one is given the barometric pressure there, one would then
need a table or have to make a calculation to get the correct setting
for the reference markers. Does this sound correct?

Dennis

Dennis

[Jon Woellhaf]

Dennis,

Can you post a photo of this altimeter's dial to, say,
alt.binaries.pictures.aviation?

Jon

[Icebound]

> wrote in message
oups.com...
> Well, I removed the innards and (independently) reset the reference
> pointers to agree with the altitude hands at the correct Kollsman
> setting. (I'm pretty handy at tinkering with delicate instruments.)
>
> But I still don't really know what those little markers are for. If, as
> you have suggested, they are used to set the altimeter to the correct
> barometric pressure when the Kollsman window is blanked out, how does
> one know where to set the markers? Let's say one is in an area where
> the altitude-barometer combination there renders the Kollsman window
> useless. If one is given the barometric pressure there, one would then
> need a table or have to make a calculation to get the correct setting
> for the reference markers. Does this sound correct?
>


Having read and re-read that article several times....

My latest take is that the correct position for them is
zero zero, when the Kollsman window set at 29.92.

From the article, they would appear to do nothing more than show the
estimated "difference" (not the "pressure altitude" as I first surmised, but
just the "difference").... the estimated difference between the *pressure*
altitude of the airport in standard-atmosphere conditions, compared to the
pressure altitude of the airport in the actual conditions of today. By
setting them to show that *difference*, your altitude readout will now show
the field elevation when you are on that field.

Left of zero would be negative (pressure altitude is less than standard,
i.e. actual pressure is higher than standard. Right of zero would be
positive, air pressure is lower than standard. ) The article mentions to
take care when setting negatives.... 900 would actually mean minus 100....


The only use of these markers would be if the station reported altimeter
setting in terms of this "pressure altitude variation", as depicted in the
diagram in the article. ( This seems to be something from a bygone era).
You would set the appropriate difference on the markers ( in the
appropriate plus or minus direction) and your altimeter would now be
adjusted correctly.....

Since pretty much everybody today reports the Kollsman value directly in
"inches of mercury" (or Millibars in Europe), you do that directly with the
Kollsman value, so the markers don't matter... you don't really care about
the "difference" any more.


So the only use today, would be... after setting the Kollsman window, you
could check a table .... or make a mental estimate.... of what the
difference should be ( about 100 feet per .10 inches of mercury away from
29.92).... Also, of course, that it is on the correct side of zero (left
side (negative) if greater than 29.92, right side if less than 29.92)....
and see that the markers correspond, as a double check.



After moving the markers to zero zero at 29.92, then setting your correct
altimeter setting, I would expect:

If, like 29.82, the indicators should show about plus 100, 29.72: plus200,
etc.
If, like 30.02: minus 100, 30.12: minus 200 , etc.

[Icebound]

"Icebound" > wrote in message
...


> .... 900 would actually mean minus 100....
>
>

.... but the "thousands" pointer would be slightly left of zero....

[Ron Parsons]

In article >,
"Icebound" > wrote:

>My latest take is that the correct position for them is
>zero zero, when the Kollsman window set at 29.92.

That is correct. If they do not, then something is mechanically wrong
within the instrument.

[[email protected]]

Jon,

Well I have a pretty good jpeg of the altimeter, but can't find the
email address for this group to post the pic to! Google says it's at
the bottom of the groups "Home Page", but I don't see it?

My groups tool (Netscape 7.0), using Google Groups, does not see
alt.binaries.pictures.aviation so I can't post there either. If you
send me your email address I'll send the pic to you. Or, if someone
knows this group's email address, I'll post the altimeter pic for all
to view.

Dennis

[Dave Butler]

wrote:
> Jon,
>
> Well I have a pretty good jpeg of the altimeter, but can't find the
> email address for this group to post the pic to! Google says it's at
> the bottom of the groups "Home Page", but I don't see it?
>
> My groups tool (Netscape 7.0), using Google Groups, does not see
> alt.binaries.pictures.aviation so I can't post there either. If you
> send me your email address I'll send the pic to you. Or, if someone
> knows this group's email address, I'll post the altimeter pic for all
> to view.

Newsgroups look like email, but they're not.

Instead of using the browser part of your Netscape 7.0, use the "mail and
newsgroups" part. It's the icon at the bottom left of your browser window that
looks like a US mail envelope, or it's the part of netscape that you use to read
email.

You might have to go to edit->preferences and configure a news server. If you
are using earthlink (as your return address indicates), use "news.earthlink.net"
as your news server. Then open the link for news.earthlink.net that is created
over on the left side of your mail and newsgroups window, click on "manage
newsgroup subscriptions" and subscribe to alt.binaries.pictures.aviation.

You might decide you want to use that to access this newsgroup, too, rather than
google.

By the way, you might want to disguise your return address when you post to
newsgroups, unless you like getting spam.

Dave

[Peter Duniho]

"Dave Butler" > wrote in message
news:1120681100.317410@sj-nntpcache-5...
> wrote:
>> [...]
>> My groups tool (Netscape 7.0), using Google Groups, does not see
>> alt.binaries.pictures.aviation so I can't post there either. If you
>> send me your email address I'll send the pic to you. Or, if someone
>> knows this group's email address, I'll post the altimeter pic for all
>> to view.
>
> Newsgroups look like email, but they're not.
>
> Instead of using the browser part of your Netscape 7.0, use the "mail and
> newsgroups" part. It's the icon at the bottom left of your browser window
> that looks like a US mail envelope, or it's the part of netscape that you
> use
> to read email.

Also, there are web services now available that will store files short-term
for transfer to other parties. They aren't a perfect solution for all
situations, and have no archive qualities (deletion of the files after a
week is common), but for quickly and easily moving files from one person to
another, they work fine.

One such service is http://www.dropload.com

For example, using the above service, upload the file, have notification
sent to yourself, and post the link here.

It's a much better solution than encoding binary files as text, even in a
newsgroup set aside specifically for that purpose (the text encoding, used
in email or in newsgroups, can add as much as 30% or so to the size of the
data being moved around...and of course, in the case of newsgroups, that
data gets copied to LOTS of places that will never actually use it).

Pete

[[email protected]]

Icebound,

Thanks for your interest and analysis. Allow me to digest it while I'm
traveling for a couple days.

BTW, a link to a pic of the altimeter should appear soon in this
discussion thread so that others can see the "extra" reference markers
the discussion centers on.

Dennis

[David Odum]

To all:

Dennis emailed me the picture of his altimeter to post to my website
so that all can see it.

http://www.AirplaneZone.com/PubDir/Alt_002.jpg (135 KB)


David Odum - email: David at AirplaneZone dot com

[Lakeview Bill]

Just from looking at the picture, I'd say the third needle is for 10,000
feet increments.

Look at how the labels line up when each pointer is in the 12:00 position...



"David Odum" <MyFirstName@AirplaneZone> wrote in message
...
>
>
> To all:
>
> Dennis emailed me the picture of his altimeter to post to my website
> so that all can see it.
>
> http://www.AirplaneZone.com/PubDir/Alt_002.jpg (135 KB)
>
>
> David Odum - email: David at AirplaneZone dot com
>

[Lakeview Bill]

Here's a modern Falcon Gauge unit with the same markings...

http://www.falcongauge.com/images/product%20images/sensitiveALT1.jpg



"David Odum" <MyFirstName@AirplaneZone> wrote in message
...
>
>
> To all:
>
> Dennis emailed me the picture of his altimeter to post to my website
> so that all can see it.
>
> http://www.AirplaneZone.com/PubDir/Alt_002.jpg (135 KB)
>
>
> David Odum - email: David at AirplaneZone dot com
>

[Blueskies]

"Lakeview Bill" > wrote in message m...
> Here's a modern Falcon Gauge unit with the same markings...
>
> http://www.falcongauge.com/images/product%20images/sensitiveALT1.jpg
>
>
>
> "David Odum" <MyFirstName@AirplaneZone> wrote in message
> ...
>>
>>
>> To all:
>>
>> Dennis emailed me the picture of his altimeter to post to my website
>> so that all can see it.
>>
>> http://www.AirplaneZone.com/PubDir/Alt_002.jpg (135 KB)
>>
>>
>> David Odum - email: David at AirplaneZone dot com
>>

You guys are missing the little black triangle just to the left of the 1000' label...does it move?

[David Odum]

" Blueskies" > wrote:


>You guys are missing the little black triangle just to the left of the 1000' label...does it move?


Just to be clear, these are the pointers in question and, according to
Dennis, they both move when the Kollsman knob is rotated but do not
move with pressure changes. The other three pointers are the standard
"sensitive altimeter" pointers familiar to most pilots.

http://www.AirplaneZone.com/PubDir/Alt_003.jpg


David - email - David at AirplaneZone dot com

[Carlos Villalpando]

In article >,
MyFirstName@AirplaneZone says...
>
> http://www.AirplaneZone.com/PubDir/Alt_003.jpg

And with the picture, it becomes somewhat clear that the pointers are
the indicating the same as the Kollsman window, but in dial form. The
white pointer is inches divided by 10 and the black pointer is the
tenths. An extra, quick to read, indicator of altimeter setting,
especially when out of range of the Kollsman window.

An experiment, put the Kollsman window on some arbitrary setting, and
see if the dials correlate to what's indicated in the window.

--Carlos V.

[David Odum]

wrote:


>Thanks for your interest and analysis. Allow me to digest it while I'm
>traveling for a couple days.

Dennis,

After reading this thread and the article that "Icebound" referenced,
I agree with Icebound's latest conjecture, the two pointers should
read zero, zero when the Kollsman dial is set to 29.92. As you have
already tinkered with the mechanism, perhaps you should tinker once
more and zero the two pointers with the Kollsman dial set to 29.92
(actually 29.92126 is more precise but of course you can't set it with
such precision). Then, if conjecture proves correct, and if the
mechanism is still working properly, the small pointers should follow
the table in the following link as you adjust the Kollsman dial.

http://www.AirplaneZone.com/PubDir/PAV.htm

The table is based on the ICAO standard atmosphere. Also note that if
the airport reports pressure altitude instead of pressure altitude
variation, and you dial in the airport pressure altitude with the two
pointers, then your altimeter should read zero (or close to zero) on
the airport ground. Perhaps this was a common practice in the early
days and, hence, the wide adjustment range of the altimeter.

Let us know what you find out when you return from your trip.

David - email: David at AirplaneZone dot com

[Blueskies]

"David Odum" <MyFirstName@AirplaneZone> wrote in message ...
>" Blueskies" > wrote:
>
>
>>You guys are missing the little black triangle just to the left of the 1000' label...does it move?
>
>
> Just to be clear, these are the pointers in question and, according to
> Dennis, they both move when the Kollsman knob is rotated but do not
> move with pressure changes. The other three pointers are the standard
> "sensitive altimeter" pointers familiar to most pilots.
>
> http://www.AirplaneZone.com/PubDir/Alt_003.jpg
>
>
> David - email - David at AirplaneZone dot com
>
>

Ha! I didn't see the little white triangle.

[Blueskies]

"Carlos Villalpando" > wrote in message
k.net...
> In article >,
> MyFirstName@AirplaneZone says...
>>
>> http://www.AirplaneZone.com/PubDir/Alt_003.jpg
>
> And with the picture, it becomes somewhat clear that the pointers are
> the indicating the same as the Kollsman window, but in dial form. The
> white pointer is inches divided by 10 and the black pointer is the
> tenths. An extra, quick to read, indicator of altimeter setting,
> especially when out of range of the Kollsman window.
>
> An experiment, put the Kollsman window on some arbitrary setting, and
> see if the dials correlate to what's indicated in the window.
>
> --Carlos V.

Looks like you got that right! It's saying something like 30.918 according to the dials while the Kollsman window says
30.902....

[Ron Parsons]

In article >,
" Blueskies" > wrote:

>"Carlos Villalpando" > wrote in message
k.net...
>> In article >,
>> MyFirstName@AirplaneZone says...
>>>
>>> http://www.AirplaneZone.com/PubDir/Alt_003.jpg
>>
>> And with the picture, it becomes somewhat clear that the pointers are
>> the indicating the same as the Kollsman window, but in dial form. The
>> white pointer is inches divided by 10 and the black pointer is the
>> tenths. An extra, quick to read, indicator of altimeter setting,
>> especially when out of range of the Kollsman window.
>>
>> An experiment, put the Kollsman window on some arbitrary setting, and
>> see if the dials correlate to what's indicated in the window.
>>
>> --Carlos V.
>
>Looks like you got that right! It's saying something like 30.918 according to
>the dials while the Kollsman window says
>30.902....

Not only do the hands rotate backwards, that's the way you read them
too. Both are showing just a hair shy of 700ft.

[Blueskies]

"Ron Parsons" > wrote in message ...
> In article >,
> " Blueskies" > wrote:
>
>>"Carlos Villalpando" > wrote in message
k.net...
>>> In article >,
>>> MyFirstName@AirplaneZone says...
>>>>
>>>> http://www.AirplaneZone.com/PubDir/Alt_003.jpg
>>>
>>> And with the picture, it becomes somewhat clear that the pointers are
>>> the indicating the same as the Kollsman window, but in dial form. The
>>> white pointer is inches divided by 10 and the black pointer is the
>>> tenths. An extra, quick to read, indicator of altimeter setting,
>>> especially when out of range of the Kollsman window.
>>>
>>> An experiment, put the Kollsman window on some arbitrary setting, and
>>> see if the dials correlate to what's indicated in the window.
>>>
>>> --Carlos V.
>>
>>Looks like you got that right! It's saying something like 30.918 according to
>>the dials while the Kollsman window says
>>30.902....
>
> Not only do the hands rotate backwards, that's the way you read them
> too. Both are showing just a hair shy of 700ft.



????????????

[Ron Parsons]

In article >,
" Blueskies" > wrote:

>"Ron Parsons" > wrote in message
...
>> In article >,
>> " Blueskies" > wrote:
>>
>>>"Carlos Villalpando" > wrote in message
k.net...
>>>> In article >,
>>>> MyFirstName@AirplaneZone says...
>>>>>
>>>>> http://www.AirplaneZone.com/PubDir/Alt_003.jpg
>>>>
>>>> And with the picture, it becomes somewhat clear that the pointers are
>>>> the indicating the same as the Kollsman window, but in dial form. The
>>>> white pointer is inches divided by 10 and the black pointer is the
>>>> tenths. An extra, quick to read, indicator of altimeter setting,
>>>> especially when out of range of the Kollsman window.
>>>>
>>>> An experiment, put the Kollsman window on some arbitrary setting, and
>>>> see if the dials correlate to what's indicated in the window.
>>>>
>>>> --Carlos V.
>>>
>>>Looks like you got that right! It's saying something like 30.918 according
>>>to
>>>the dials while the Kollsman window says
>>>30.902....
>>
>> Not only do the hands rotate backwards, that's the way you read them
>> too. Both are showing just a hair shy of 700ft.
>
>
>
>????????????

In this case I should have said -700 which is how much the pressure is
higher than sea level standard.

When set to zero the window reads 29.92 and the altimeter reads pressure
altitude. Conversely, when they are set to pressure altitude, the
altimeter reads zero.

[Icebound]

"Lakeview Bill" > wrote in message
m...
> Here's a modern Falcon Gauge unit with the same markings...
>
> http://www.falcongauge.com/images/product%20images/sensitiveALT1.jpg
>


Where are they? I cannot spot any markers in your pic other than the 3
indicated-altitude pointers.

The moving indicators that dennise9 is writing about, are the tiny triangles
at the 3, and just to the right of the nine.... reading minus-700 in the
pic, as per the article which I posted about earlier. Since (s)he has
moved them independently of the Kollsman Knob (partly in response to my
speculation, I must confess), they are probably slightly in error for the
altimeter setting shown ( 30.90 )... I would expect closer to -1000 (or the
outer pointers at 0 and the inner on the 9)

So I am recommending putting the Kollsman at 29.92, resetting the markers
independently to zero zero, and then we would see if they go to near -1000
(as I would expect), when the Kollsman is put back to 30.92.

Or, if (s)he has already reset the pointers to zero-zero at 29.92, then -700
might just be a more accurate reflection of the 1.00 inch change in
altimeter setting between 29.92 and 30.92, than is the usual rule-of-thumb:
100 feet per .1 inch in altimeter setting.

[Carlos Villalpando]

In article >,
says...

> In this case I should have said -700 which is how much the pressure is
> higher than sea level standard.

Hmm..... That's almost 200 feet off of what the difference actually is,
wich is something just shy of -900 or so, from memory, between 2992 and
3090. If that's it, the altimeter's scale factors are way off. Though
your explaination makes sense if they go negative above 2992 and
positive below 2992.

> When set to zero the window reads 29.92 and the altimeter reads pressure
> altitude. Conversely, when they are set to pressure altitude, the
> altimeter reads zero.

How about a request. A series of images. Pick a day, tell us the
altitude of the desk that the altimeter is sitting on, set it to the
local altimeter setting and take a series of pictures of that setting,
plus a few tenths above and below.

Then another series at 2992, plus a few tenths above and below if they
don't overlap too badly with the first series.

And if you're really a glutton for punishment and have free time to
waste, a series at 2992, but in an airplane at several altitudes.

Then somebody is bound to figure out what they really do.

--Carlos V.

[RomeoMike]

The little black triangle look like an altitude bug. It looks like it
can be moved around to whatever position you choose. But then I haven't
read the whole thread to know if that's true.
>>>
>
>
> You guys are missing the little black triangle just to the left of the 1000' label...does it move?
>
>

[[email protected]]

Icebound wrote:
> "Lakeview Bill" > wrote in message
> m...
> > Here's a modern Falcon Gauge unit with the same markings...
> >
> > http://www.falcongauge.com/images/product%20images/sensitiveALT1.jpg
> >
>
>
> Where are they? I cannot spot any markers in your pic other than the 3
> indicated-altitude pointers.
>
> The moving indicators that dennise9 is writing about, are the tiny triangles
> at the 3, and just to the right of the nine.... reading minus-700 in the
> pic, as per the article which I posted about earlier. Since (s)he has
> moved them independently of the Kollsman Knob (partly in response to my
> speculation, I must confess), they are probably slightly in error for the
> altimeter setting shown ( 30.90 )... I would expect closer to -1000 (or the
> outer pointers at 0 and the inner on the 9)
>
> So I am recommending putting the Kollsman at 29.92, resetting the markers
> independently to zero zero, and then we would see if they go to near -1000
> (as I would expect), when the Kollsman is put back to 30.92.
>
> Or, if (s)he has already reset the pointers to zero-zero at 29.92, then -700
> might just be a more accurate reflection of the 1.00 inch change in
> altimeter setting between 29.92 and 30.92, than is the usual rule-of-thumb:
> 100 feet per .1 inch in altimeter setting.


Wow, what a group! I never expected such discission on my old
altimeter. Thanks! From the posts, it makes me think that I have a real
antique here with three hands and two "reference markers". After
reading all your posts, together with Iceman's excellent link and
comments, my conclusion is this.

The reference markers are simply the "altitude equivalent" of the
pressure in the Kollsman window, referenced to zero-zero at 29.92. The
markers show positive altitudes (CW = positive) for Kollsman settings
lower than 29.92 and negative (CCW = negative) altidudes for Kollsman
settings above 29.92.

With the reference markers set to zero-zero at 29.92,at my present
location (about 5,300 ft above sea level), a manual 1 inch Kollsman
change to 28.92 gives a reference marker indication of about +940 feet.
A manual 1 inch Kollsman change to 30.92 shows a reference marker
indication of about minus 920 feet. I can't explain why a 1 inch change
above and below 29.92 doesn't give the same absolute altitude change
e.g. +920 ft, and -920 ft. Instead I get +940 ft. and -920 ft.

In todays times, as someone has mentioned, the only use I can see for
the markers is as follows. For situations when the Kollsman wndow is
'blanked out' one could take the local given pressure, convert that
into an equivalent altitude, dial it in with the reference markers,
then read the correct altitude above MSL from the normal hands.

Dennis

[Icebound]

> wrote in message
oups.com...
>
> Wow, what a group! I never expected such discission on my old
> altimeter. Thanks! From the posts, it makes me think that I have a real
> antique here with three hands and two "reference markers". After
> reading all your posts, together with Iceman's excellent link and
> comments, my conclusion is this.
>
> The reference markers are simply the "altitude equivalent" of the
> pressure in the Kollsman window, referenced to zero-zero at 29.92. The
> markers show positive altitudes (CW = positive) for Kollsman settings
> lower than 29.92 and negative (CCW = negative) altidudes for Kollsman
> settings above 29.92.
>
> With the reference markers set to zero-zero at 29.92,at my present
> location (about 5,300 ft above sea level), a manual 1 inch Kollsman
> change to 28.92 gives a reference marker indication of about +940 feet.
> A manual 1 inch Kollsman change to 30.92 shows a reference marker
> indication of about minus 920 feet. I can't explain why a 1 inch change
> above and below 29.92 doesn't give the same absolute altitude change
> e.g. +920 ft, and -920 ft. Instead I get +940 ft. and -920 ft.
>

It *is* explainable and consistent.

The difference between 29.92 and 30.92 is within a *higher* average pressure
range, and hence denser air, and hence a change from one pressure level to
another is actually a *smaller* altitude change. Between 29.92 and 28.82,
it is a *lower* average pressure, less dense air, and so you have to go
farther in order to get the same 1.00 pressure change.... apparently about
20 feet farther, according to your instrument.

[Ron Parsons]

In article . com>,
wrote:

> In todays times, as someone has mentioned, the only use I can see for
>the markers is as follows. For situations when the Kollsman wndow is
>'blanked out' one could take the local given pressure, convert that
>into an equivalent altitude, dial it in with the reference markers,
>then read the correct altitude above MSL from the normal hands.

The use was to set field pressure Altitude on the reference markers so
that your altimeter reads QFE... that is altitude above Field Elevation.

Simplifies flying the pattern at 800ft, 1500, or what ever is normal for
your airport, but the real use is for approach where your minimums are
200 ft... instead of looking for a DH of 5,500, you would be looking for
200.

American and Eastern used them this way for decades. In older aircraft,
one altimeter was set to QNH and the other to QFE for approach. Later, a
third altimeter was installed and both pilots would look at QFE on
approach.

When you only fly to one or two airports in a day, it's not that big a
deal, but when you are making 6 to 8 landings with low ceilings,
descending to the 200, 300, 400, or whatever is on the plate simplifies
things a lot.

Over the long haul, it's nicer to find concrete than foliage.